It's hard to argue that Naruto isn't one of the most iconic shonen manga heroes ever created. He and Sasuke are instantly recognizable, even to those who haven't read or watched the global sensation. Despite their status as icons though, there's one other ninja who actually deserves the spot of protagonist much more than either Naruto or Sasuke.
One way to track how important a character is in a series is by how connected they are to the rest of the series' cast. Looking at Naruto through this lens, it's easy to see why Naruto and Sasuke are the story's heroes. Almost every single important character in the series has some sort of relationship to Naruto, Sasuke, or both. Naruto and Sasuke's reincarnation twist even gives them a connection to characters who died long before they did. This separates the two of them from other important characters like Sakura. While there are a few characters who Sakura knows that Naruto doesn't, they are few and often aren't important to the larger plot. Meanwhile, everyone Sasuke knows that Naruto doesn't (such as Itachi) play a much bigger role in the broader narrative. Still though, there's one hero who is more connected to the series' cast than Naruto and Sasuke; their teacher Kakashi.
Most major characters in Naruto have some sort of relationship to Kakashi. He trained Team 7, has a working relationship with the other Team leaders, was trained by Naruto's father Minato, and worked with Itcahi in ANBU. Additionally, Kakashi's iconic Sharingan was actually taken from his best friend Obito... who would eventually become one of the series' most important antagonists as he directly manipulated the actions of the Akatsuki which set much of the series' actions into motion. But deeper than just his connection to others in the story, Kakashi has a story that is just as compelling as Naruto or Sasuke's... if not more so. Kakashi's father was a god-tier ninja who was vilified by Konoha for saving the lives of his companions over completing a mission.
Overall, when looking at Kakashi's story and his connections to others, it's clear that his life embodies every theme Naruto attempts to tackle throughout its run. His status as a genius and his relationship with Might Guy encapsulates hard work vs. natural talent, his father's story highlights what it truly means to be a social outcast, and his and Obito's shared trauma shows how much hate can warp and twist a person.
While Naruto and Sasuke are good protagonists and have earned their iconic status, Kakashi is arguably more popular with the series' fans. There's a good reason Kakashi got his own Naruto spinoff book. His connection to others and tragic backstory should mark Kakashi as the true hero of Naruto.